U.S. patent number 4,731,680 [Application Number 06/943,751] was granted by the patent office on 1988-03-15 for disk drive with stored positioning data related to disk expansion.
This patent grant is currently assigned to Victor Company of Japan, Ltd.. Invention is credited to Keiichi Kaneko, Masakatsu Moriyama.
United States Patent |
4,731,680 |
Moriyama , et al. |
March 15, 1988 |
Disk drive with stored positioning data related to disk
expansion
Abstract
A disk drive apparatus includes apparatus for elimination of
off-track errors of a read/write head by deriving and storing
correction data for all of the tracks on a disk on the basis of the
signal level resulting from read-out of the contents of gap
portions of the format data in two specific tracks. If, as
indicated by a read error indication signal from a host computer,
read errors subsequently occur in spite of position correction
based on a stored correction value, then the off-track error for
the track concerned is detected and an updated correction value is
derived and stored. Accurate position control is thereby attained
without a need for servo data tracks or regions to be recorded on
each disk.
Inventors: |
Moriyama; Masakatsu (Yokohama,
JP), Kaneko; Keiichi (Yokohama, JP) |
Assignee: |
Victor Company of Japan, Ltd.
(JP)
|
Family
ID: |
17678421 |
Appl.
No.: |
06/943,751 |
Filed: |
December 19, 1986 |
Foreign Application Priority Data
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|
|
|
|
Dec 19, 1985 [JP] |
|
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60-284428 |
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Current U.S.
Class: |
360/78.13;
G9B/5.195; 318/634; 360/99.08 |
Current CPC
Class: |
G11B
5/556 (20130101) |
Current International
Class: |
G11B
5/55 (20060101); G11B 021/08 (); G11B 021/10 () |
Field of
Search: |
;360/77,78,75
;318/685,696,634,632,561 ;364/170,571 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
IBM TDB vol. 19, No. 3, "Track Location Correction Mechanism for
Magnetic Disks", Hanson et al., 8/76, pp. 1039-1042. .
"Refined Closed-Loop Servo Enhances Low-Cost Drive's Accuracy", by
Larry Sarisky; Electronics/Mar. 10, 1983, pp. 139-142..
|
Primary Examiner: Cardillo; Raymond F.
Assistant Examiner: Garland; Steven R.
Attorney, Agent or Firm: Lowe, Price, LeBlanc, Becker &
Shur
Claims
What is claimed is:
1. A disk drive apparatus comprising:
a read and write head for writing and reading data to and from
respective ones of a plurality of concentric track successively
formed with a fixed track pitch on a surface of a recording disk,
each of said tracks including at least one fixed data portion
having predetermined fixed data written therein;
a spindle motor for rotating said recording disk;
an access motor coupled to said read and write head for displacing
said read and write head radially with respect to said recording
disk above said recording disk surface;
detection means for detecting a level of a read signal produced by
said read and write head during read-out of said data written in
said at least one fixed data portion, and for producing a detection
signal representing said signal level, and;
computation and control circuit means including memory means,
operable to execute a correction data acquisition operation by:
(a) controlling said access motor to move said read and write head
to a first predetermined standard position of a first track of a
predetermined pair of said plurality of tracks, said first track of
said predetermined pair being positioned close to an outer
periphery and a second track of said predetermined pair being
positioned close to an inner periphery of said plurality of tracks,
and to then radially displace said read and write head relative to
said first standard position within a predetermined range of
movement, said computation and control means then determining an
amount of off-track error of said read and write head with respect
to said first standard position of said first track based upon
changes in said detection signal occurring during said radial
displacement of the read and write head with respect to the first
track;
(b) controlling said access motor to move said read and write head
to a second predetermined standard position of a second one of said
pair of tracks and to then radially displace said read and write
head relative to said second standard position within a
predetermined range of movement, said computation and control means
then determining an amount of off-track error of said read and
write head with respect to said second standard position of said
second track based upon changes in said detection signal occurring
during said radial displacement of the read and write head with
respect to the second track, and;
(c) storing in said memory means said off-track error amounts for
said pair of tracks as respective correction values, and computing
and storing in said memory means respective correction values for
each of the other ones of said plurality of tracks based upon said
off-track error amounts determined for said first and second
tracks;
said computation and control circuit means subsequently functioning
to correctly position said read and write head in response to an
externally supplied request for access to one of said tracks, by
reading out from said memory means the one of said correction
values corresponding to the requested track and then controlling
said access motor to move said read and write head to a position
which is radially displaced from the standard position of the
requested track in a direction and by an amount which are in
accordance with said corresponding correction value.
2. A disk drive apparatus according to claim 1, in which said
access motor is a stepping motor operable both in a stepping mode
of operation in which said read and write head is moved by radial
step displacements, with said track pitch being an integral
multiple of one of said step displacements, and in a microstepping
mode of operation in which said read and write head is moved by
radial microstep displacements each of amplitude substantially
smaller than said track pitch.
3. A disk drive apparatus according to claim 2, in which said
radial displacement of said read and write head relative to one of
the first or second standard positions during said correction data
acquisition operation is executed as a fixed number of successive
ones of said microstep displacements from the standard position of
said one of the first or second tracks in one direction, followed
by a fixed number of microstep displacements from said standard
position of said one of the first or second tracks in the opposite
direction.
4. A disk drive apparatus according to claim 3, in which said
computation and control means executes said read and write head
positioning in response to said request for access to a track by
first controlling said access motor to move said read and write
head to a standard position of said requested track by operation in
said stepping mode, said computation and control means then reading
out from said memory means the one of said correction values
corresponding to said requested track and controlling said access
motor to operate in said microstepping mode to move said read and
write head from said standard position of said requested track by a
number of said microstep displacements and in a radial direction
which are respectively in accordance with said correction
value.
5. A disk drive apparatus according to claim 2, in which said
access motor is a two-phase stepping motor, and in which operation
in said microstepping mode is executed by fixing a level of a first
current phase supplied to said motor at a constant value while
decrementing the level of a second current phase supplied to said
motor in successive steps, with said steps successively varying in
amplitude in accordance with a tangent characteristic.
6. A disk drive apparatus according to claim 1, in which said
request for access to a track is issued as a signal supplied from a
host computer, said data read from said disk being supplied to said
host computer, and in which said host computer responds to an
occurrence of errors in data which is read out from a track, while
said read and write head is positioned relative to said track in
accordance with the corresponding one of said stored correction
values, by issuing an error indication signal to said disk drive
apparatus, said computation and control means responding to said
error indication signal by:
controlling said access motor to radially displace said read and
write head relative to the standard position of the one of said
tracks from which said data errors were read, within said
predetermined range of movement, said computation and control means
then determining an amount of off-track error of said track based
upon changes in said detection signal occurring during said
displacement;
storing said off-track error amount in said memory means as an
updated correction value to replace said corresponding stored
correction value, and;
reading out from said memory means said updated correction value
and controlling said access motor to move said read and write head
to a position which is radially displaced from the standard
position of said track by an amount and in a direction which are
respectively in accordance with said updated correction value.
7. A disk drive apparatus according to claim 1, in which said
detection means comprise:
index pulse generating means for producing index pulses in
synchronism with times during which said data of said gap portions
of a track is being read by said read and write head and a
corresponding read signal produced thereby;
sample-and-hold circuit means for sampling and holding an amplitude
of pulses in said read signal at timings determined by said index
pulses, and;
analog-digital conversion means for converting an analog output
signal from said sample-and-hold circuit means to a digital signal
representing said pulse amplitude, said digital signal constituting
said detection signal.
8. A disk drive apparatus according to claim 1, and further
comprising insertion sensing means responsive to insertion of a
recording disk into said disk drive apparatus for producing an
output signal, and in which said computation and control means is
responsive to said insertion means output signal for initiating
said correction data acquisition operation.
9. A disk drive apparatus according to claim 1, and further
comprising temperature sensing means for producing an output signal
in response to a change in temperature within said disk drive
apparatus which exceeds a predetermined amount, and which said
computation and control means is responsive to said temperature
sensing means output signal for initiating said correction data
acquisition operation.
10. A disk drive apparatus according to claim 1, and further
comprising humidity sensing means for producing an output signal in
response to a change in humidity within said disk drive apparatus
which exceeds a predetermined amount, and in which said computation
and control means is responsive to said humidity sensing means
output signal for initiating said correction data acquisition
operation.
11. A disk drive apparatus according to claim 1, and further
comprising timer means for producing an output signal each time a
predetermined time interval has elapsed, and in which said
computation and control means is responsive to said timer means
output signal for initiating said correction data acquisition
operation.
12. A disk drive apparatus for reading data from a plurality of
concentric tracks of a recording disk and for supplying said data
to a host computer, said host computer functioning to detect the
presence of errors in said data and to supply to said disk drive
apparatus an error indication signal indicative of such errors,
each of said tracks including a gap fixed data portion having fixed
data written therein, said disk drive apparatus comprising:
a read and write head for read-out of said data from said
tracks;
means for rotating said disk;
means for positioning said read and write head with respect to said
tracks along a radius of said disk;
detection means for detecting a level of a read signal produced
from said read and write head during read-out of said fixed data
from said fixed data portion of a track and for producing a
corresponding detection signal, and;
computation and control means including memory means, operable to
execute a correction data acquisition operation by detecting an
amount of off-track error of said read and write head with respect
to at least one of said tracks based upon said detection signal,
computing respective correction values for the remainder of said
tracks based on said detected off-track error amount, and storing
in said memory means said correction values;
said computation and control means further functioning to control
said read and write head positioning means prior to read-out of
data from one of said tracks such as to accurately position said
read and write head with respect to said track based upon a
corresponding one of said stored correction values, and further
functioning, in the event that said error indication signal is
produced from said host computer during subsequent read-out of data
from said track following said accurate positioning, to execute a
single track correction data acquisition operation for said track
and to store as an updated correction value for said track an
off-track error which is derived by said single track correction
data acquisition operation, and to control said read and write head
positioning means to accurately position said read and write head
in accordance with said updated correction value.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a disk drive apparatus for
computer or other data processing applications, whereby automatic
correction of off-track errors of a read/write head with respect to
recording tracks formed on a surface of the disk is implemented,
without the necessity to provide dedicated servo tracks or embedded
servo data regions on the disk.
In recent years there has been a trend towards increasing the
density of tracks which are provided on recording disks of the type
generally referred to as "floppy disks". These are formed as
flexible sheets and are used as an external recording medium for
computers etc. To attain higher track densities, there is a
requirement for an increase in the accuracy to which the read/write
head (generally an electromagnetic head) used with such a disk will
follow the recording tracks upon the disk, i.e. a requirement for
elimination of off-track errors (that is, errors between the actual
radial position of a read/write head and the optimum position of
that head with respect to a track). Various tracking servo systems
have been proposed in the prior art, for increasing this tracking
accuracy. With one such system, outer and inner dedicated servo
tracks are respectively provided around the outer periphery and
inner periphery of the data tracks which are recorded on the disk,
while in addition an optical scale is incorporated. The optical
scale is used to accurately detect the position of the read/write
head with respect to the reference tracks, whereby compensation is
executed for any off-track error of the read/write head
position.
With another known method employing inner and outer dedicated servo
tracks, a stepper motor having a fine step adjustment capability is
employed to move the read/write head. When a disk is newly set in
the apparatus, the head is first moved into position over the outer
servo track, and fine step adjustment is then performed to position
the head directly over that track, by a servo positioning loop
which functions on the basis of the amplitude of a signal which is
read out from the head. The head is then moved to the inner servo
track, and servo operation is again performed, to position the head
directly over that track. The amount of fine adjustment of the head
position which is required to align the head directly above the
inner and outer servo tracks is thereafter utilized as data for
determining amounts of fine adjustment which must be performed for
each of the data tracks, to attain accurate head positioning for
each track.
With another tracking servo method which is known in the prior art,
a train of pulse signals are recorded as servo data in a
predetermined region in each of the data tracks, i.e. as embedded
servo data. The read signal level which results from reproduction
of these pulse signals is compared with a reference level, whereby
the amount of off-track error and the direction of that error can
be detected. Compensation for this off-track error is performed by
tracking servo operation.
With the prior art tracking servo arrangements describe above, it
is necessary that dedicated servo tracks or embedded servo data
regions be recorded beforehand upon each of the disks. This leads
to increased manufacturing cost, and in addition such a method
renders it impossible to utilize disks which do not have such
dedicated servo tracks or embedded servo data regions recorded
thereon. Furthermore, if such special disks are employed, then if
the dedicated servo tracks or embedded servo data regions are
inadvertently erased, tracking servo operation will no longer be
possible.
Also, in the case of the second prior art method described above,
continuous servo operation is not performed after the initial
correction data has been obtained, based on the inner and outer
servo tracks. Thus, any variation in recording track position which
cannot be determined from that initial correction data (e.g. a
shift in track position due to thermal expansion, for example)
cannot be corrected with such a system.
The various sources and amounts of off-track error are graphically
illustrated in FIG. 2. As shown, these include radial expansion and
contraction of the disk due to changes in temperature or humidity,
deviations in dimensions of different read/write heads (i.e.
between different disk drive units), etc. However as can be
understood from FIG. 2, the major source of off-track error is
radial expansion and contraction of the disk, which can result in
large amounts of off-track error along a direction extending from
the inner periphery to the outer periphery of the disk recording
area.
It can thus be understood that it is essential, for a disk drive
apparatus providing a very high recording track density, to
continuously monitor the position of the read/write head with
respect to a track which is currently being accessed.
SUMMARY OF THE INVENTION
It is an objective of the present invention to overcome the
problems of the prior art described above, and to provide a disk
drive apparatus which does not require that any form of dedicated
servo tracks or embedded servo data regions be recorded upon disks
which are utilized by the apparatus, yet whereby a track density
can be attained which has only been possible in the prior art by
means of such dedicated servo tracks or embedded servo data regions
utilized in conjunction with servo control systems for eliminating
tracking errors.
To attain this objective, a disk drive apparatus according to the
present invention includes means for measuring respective amounts
of off-track error for each of two tracks which are respectively
positioned at (or near) the inner and outer peripheries of the
recording track area of a disk. These error amounts are then stored
as correction values for these tracks, and are also employed in
computing respective correction values for all of the other tracks.
When a track is subsequently accessed, the position of the
read/write head is correctly established on the basis of the
corresponding correction value, thereby eliminating the off-track
error for that track. Furthermore, if the host computer should
detect the presence of read errors during read-out of data from a
track, and issues a read error indication, then the system
functions to derive an updated corrrection value for that track and
to re-position the head in accordance with that updated value.
More specifically, a disk drive apparatus according to the present
invention comprises:
a read and write head for writing and reading data to and from
respective ones of a plurality of concentric track successively
formed with a fixed track pitch on a surface of a recording disk,
each of the tracks comprising format data which includes at least
one gap portion having predetermined fixed data written
therein;
a spindle motor for rotating the recording disk;
an access motor coupled to the read and write head for displacing
the read and write head radially with respect to the recording disk
above the recording disk surface;
detection means for detecting a level of a read signal produced by
the read and write head during read-out of the data written in the
gap portions, and for producing a detection signal representing the
signal level, and;
computation and control circuit means including memory means,
operable to execute a correction data acquisition operation by:
(a) controlling the access motor to move the read and write head to
a predetermined standard position of a first track of a
predetermined pair of the plurality of tracks, the pair being
respectively positioned close to an outer periphery and close to an
inner periphery of the plurality of tracks, and to then radially
displace the read and write head relative to the standard position
within a predetermined range of movement, the computation and
control means then determining an amount of off-track error of the
read and write head with respect to the standard position of the
first track based upon changes in the detection signal occurring
during the radial displacement of the read and write head with
respect to the first track;
(b) controlling the access motor to move the read and write head to
a predetermined standard position of a second one of the pair of
tracks and to then radially displace the read and write head
relative to the standard position within a predetermined range of
movement, the computation and control means then determining an
amount of off-track error of the read and write head with respect
to the standard position of the second track based upon changes in
the detection signal occurring during the radial displacement of
the read and write head with respect to the second track, and;
(c) storing in the memory means the off-track error amounts for the
pair of tracks as respective correction values, and computing
respective correction values for each of the other ones of the
plurality of tracks based upon the off-track error amounts
determined for the first and second tracks;
the computation and control circuit means subsequently functioning
to correctly position the read and write head in response to an
externally supplied request for access to one of the tracks, by
reading out from the memory means the one of the correction values
corresponding to the requested track and then controlling the
access motor to move the read and write head to a position which is
radially displaced from the standard position of the requested
track in a direction and by an amount which are in accordance with
the corresponding correction value.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a general block diagram to illustrate the basic elements
of a disk drive apparatus according to the present invention;
FIG. 2 is a diagram for graphically illustrating the relationship
between radial position along a disk and the effects of various
sources of off-track error;
FIG. 3 is a block circuit diagram of an embodiment of a disk drive
apparatus according to the present invention;
FIG. 4 is a diagram illustrating the signal recording format of a
disk for use with the embodiment of FIG. 3;
FIG. 5 is a diagram illustrating a relationship between
microstepping displacement of a read/write head in the embodiment
of FIG. 3 and read signal level output from the head, and;
FIG. 6 is a diagram illustrating a relationship between
microstepping displacement and drive current levels of an access
motor in the embodiment of FIG. 3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is a simplified block diagram to illustrate the essential
components of a disk drive apparatus according to the present
invention. Numeral 1 denotes an access motor which is coupled by a
rack 10 and pinion 11 to move a read/write head 2 along a radius of
a disk 3, writing and reading signals to and from disk 3. Read and
write data are transferred to and from a host computer (not shown)
via a terminal 2a. Access motor 1 is a stepping motor which is
capable of both normal stepping operation, (i.e. rotation in
successive step rotation increments which by successive drive
current polarity alternations) and microstepping operation. In the
present specification and claims, "microstepping" has the
significance of rotation in successive fine steps, i.e.
"microsteps" each of which is substantially smaller than the step
amplitude during normal stepping operation. Numeral 4 denotes a
detection section, for detecting an amount of off-track error of
read/write head 2 with respect to tracks which are formed on disk
3. This detection is performed on the basis of the amplitude of
signals produced by read-out of a predetermined region of the
format data, which is beforehand recorded upon such disks at
standardized positions on each data track. The apparatus further
includes a computation and control section 5, which functions to
compute respective correction quantities for all of the tracks on
disk 3 and to perform overall control functions. These correction
quantities are based upon stored data obtained from output signals
S1, which are produced from detection section 4 during a correction
data acquisition operation which is executed when a disk is newly
set into the apparatus. During this correction data acquisition
operation, the read/write head 2 is moved to the approximate
position of one of at least two tracks designated as OT and IT,
which are formed on disk 3. Based on the amplitude of a signal
which is read out of a format portion of this track, by the
read/write head 2, the detection section 4 detects an amount and
direction of positional error between the read/write head 2 and the
selected OT or IT track, and produces signals S1 representing this
error, which are applied to the computation and control section 5.
The read/write head 2 is then moved to the approximate position of
the other one of tracks OT and IT, and the above process is
repeated. Based on the amounts of positional error which have thus
been found for tracks OT and IT, the computation and control
section 5 computes respective correction values for each of the
other tracks on disk 3, and stores these values in predetermined
addresses of a memory. The amounts of error found for tracks OT and
IT represent, in themselves, the correction values for tracks OT
and IT, and are stored accordingly.
It is an essential feature of the present invention that these two
tracks OT and IT are exactly identical, in function and format, to
all of the other data tracks on the disk. That is to say, the
positions of tracks OT and IT are established, as are the positions
of all of the other tracks, during initial formatting of the disk,
i.e. the process of writing format data (described hereinafter)
upon the disk, and tracks OT and IT can be utilized for writing and
reading data in the same way as all of the other tracks on the
disk. It is therefore not necessary to use dedicated servo tracks
or embedded servo data regions in the tracks, so that an apparatus
according to the present invention is completely compatible with
disks which have been recorded on other types of disk drive
apparatus which conform to the same disk format standards.
After initial correction data acquisition has been executed as
described above, correction signals S2 are produced by the
computation and control section 5 when a data track is accessed,
with these signals S2 being generated in accordance with the stored
correction quantitity for that track. These correction signals S2
are applied to a rotation control section 6, which controls the
access motor 1. To access a desired track, data which identifies
the required track is applied from the host computer, through an
input terminal 6a, to the rotation control section 6. Rotation
control section 6 then drives the access motor 1, by a specific
number of steps, to a predetermined standard position of the
required track. Microstep operation of access motor 1 is then
executed by rotation control section 6, based upon the correction
signals S2 produced from the computation and control section 5, to
thereby precisely position the read/write head with respect to the
track which is to be accessed.
It is another essential feature of the present invention that,
thereafter, a form of position servo control operation is executed,
to maintain the read/write head correctly aligned over the track
which is being accessed. This servo control is based upon a "read
error" indication signal, which is produced from the host computer
in the event that errors are detected in the data which is read out
from the track being accessed. This read error indication signal is
applied from the host computer, to the computation and control
section 5. In response, the computation and control section
initiates a new correction date acquisition process, to obtain a
new correction value which represents the actual amount of
positional error between the read/write head and the track which is
being accessed. This correction value is then stored, replacing the
previously stored correction value for that track, and the
computation and control section 5 produces a correction signal S2
in accordance with the new correction quantity, which causes the
rotation control section 5 to position the read/write head
precisely with respect to the track which is being accessed.
It can thus be understood that, with the present invention,
error-free operation will be maintained in spite of the effects of
expansion or contraction of the disk, but that it is not necessary
to employ dedicated servo control tracks or embedded servo data
regions to ensure such error-free operation. In this way, off-track
error amounts can be held to extremely low levels, so that track
density and hence recording density can be substantially increased,
while maintaining complete compatibility with disks recorded on
other types of apparatus.
A detailed description of an embodiment of a disk drive apparatus
according to the present invention will now be given. FIG. 3 is a
block diagram of this embodiment, in which signals are transferred
between the disk drive apparatus and the host computer through a
port 12. The computation and control section 5 consists of an input
port 52, an output port 53, a CPU (central processing unit) 51, a
counter circuit 57, a pulse generating circuit 56, a ROM (read-only
memory) 54, and a RAM (random access memory) 55. MOT denotes a
track which is formed at the outermost periphery of the recording
area of a disk 3 which is rotated by a spindle motor 7, while MIT
denotes a track formed at the innermost periphery of that recording
area. As stated above with reference to FIG. 1, these tracks MOT
and MIT are in all respects identical in format to all of the other
tracks on the disk, and are used for normal data read/write
purposes. Respective amounts of off-track error of the read/write
head 2 with respect the MOT and MIT tracks are detected by
detection section 4, in accordance with the amplitude of a format
data read signal, as described hereinafter. These amounts of
off-track error represent values of correction which must be
applied to the radial position of the read/write head 2 in order to
align the head optimally with respect to the MOT and MIT tracks
respectively, and are stored in RAM 55 of computation and control
section 5. In addition, based on these off-track error quantities
detected for the MIT and MOT tracks, respective correction values
for each of the other tracks on disk 3 are computed by the
computation and control section 5, and stored in RAM 55. These
stored correction values will be collectively referred to as
H.sub.N. This completes a correction data acquisition process,
which is executed when a disk 3 is set on the disk drive apparatus,
during a time in which the disk is rotating but is not currently
being accessed by the host computer.
Subsequently, when a track on the disk 3 is to be accessed, data
designating the required track (indicated as D.sub.t in FIG. 3) is
supplied from the host computer to the computation and control
section 5 and the rotation drive section 6. The rotation drive
section 6 then controls stepping operation of access motor 1 to
move the read/write head 2 to a predetermined standard position of
the required track. The correction value corresponding to that
track is then supplied from the computation and control section 5
to the rotation drive section 6, which responds by controlling
access motor 1 to execute microstepping operation in accordance
with the correction value, whereby the read/write head 2 becomes
positioned optimally with respect to the desired track.
The above positioning operations are performed prior to the time at
which data transfer between the host computer and the read/write
head 2 commences. Subsequently, after this data transfer has
commenced, it is possible that off-track errors may occur during
access to the selected track, in spite of the position correction
operation described above. Such errors can arise for example due to
thermal expansion or contraction of the disk. An off-track error
will be detected by the host computer during read-out of data from
the disk 3, based on the contents of the read data, and a read
error indication signal will be generated by the host computer,
which is supplied to the computation and control section 5. The
computation and control section 5 responds by executing an
internally stored program, whereby microstepping advancement of the
read/write head 2 is performed across the position of the track in
question. An off-track error quantity for that track is thereby
determined by the error detection section 4, and is stored as an
updated correction value for that track, replacing the previously
derived correction value. The read/write head 2 is then
repositioned above the required track, microstep adjustment of the
head position is executed based on the updated correction value,
and accessing of the track by the host computer is recommenced.
In this way, correction is applied to compensate for any special
source of error which may affect particular tracks on the disk.
During normal stepping operation, the rotation drive section 6
preferably controls the access motor 1 to move the electromagnetic
head 2 along a radius of disk 3 in steps which each have an
amplitude equal to one track pitch, or in steps which each have an
amplitude equal to a plurality of track pitches.
Furthermore, the disk 3 is preferably formed with a surface
consisting of, for example, PET (polyethylene terethalate) which is
coated with Fe powder, to thereby constitute a high-density
recording medium. The overall diameter of the disk 3 in this
embodiment is approximately 88.6 mm, and the total number of tracks
formed on the disk is 160, so that the track density is 270.933
tpi.
FIG. 4 is a diagram to illustrate the format in which signals are
recorded on disk 3. Each track is divided into 47 sectors, with
these sectors extending between gap portions designated as GAP 1
and GAP 4. As used in the present specification and claims, the
term "gap portion" has the meaning of a portion of a track within
which is recorded a predetermined fixed pulse sequence, and which
serves as a buffer region between data recording regions. Each
sector has the configuration shown in FIG. 4, consisting of two
synchronization signal portions (SYNC), an identification field ID,
gaps GAP 2 and GAP 3, and a data field (DATA). The ID field
consists of an ID address (IDAM), a cylinder number (CYL), a head
number (HD), an error correction code (CRC), and a sector number
(SEC). In FIG. 4, the numbers enclosed in parentheses indicate the
number of bytes recorded in each field. The various portions shown
in FIG. 4, except for the data field, are recorded on
formatting.
The disk 3 is rotated by a spindle motor 7 at a relatively high
speed of rotation (e.g. 1200 rpm).
Linear displacement of the electromagnetic head 2 is achieved by a
drive force which is applied from the access motor 1, acting
through a rack 10 and a pinion 11, whereby electromagnetic head 2
is moved radially across the disk 3.
Readout and write-in of signals from/to disk 3 are performed by
data transfer between the host computer and electromagnetic head 2
through a data signal I/O terminal 13 of an input/output port 12.
The data is transferred to/from the host computer via a controller
(not shown in the drawings).
A read output signal S3 produced by the electromagnetic head 2 is
supplied via a read/write circuit 41 to the detection section 4,
which consists of a sample-and-hold circuit 42, and an A/D
(analog-to-digital) converter 43. The read output signal S3 is
amplified by amplifier 41, and the output signal thus produced is
supplied to terminal 13 of port 12 and also to the sample-and-hold
circuit 42. The sample-and-hold circuit 42 is coupled to receive
index pulses P1 as hold pulses. These index pulses P1 are
respectively produced in synchronism with successive revolutions of
the disk 3, and have a timing relationship to the format data on
the disk as shown in FIG. 4. The pulses P1 are generated in this
embodiment through detection performed by a photo-coupler (formed
of a light-emitting element 14 and a photo-sensing element 15) of
light which is reflected from a reflector member 31, mounted on the
shaft of spindle motor 7. The relative positions of the
photo-coupler and reflector 31 are established such that each pulse
P1 is generated at the commencement of read-out of the GAP 1
portion of the track which is currently being read (as shown in
FIG. 4). The GAP 1 portion contains 52 bytes, consisting of
repetitions of the hexadecimal number [4E].sub.16. In this way, the
sample-and-hold circuit 42 performs hold operations in
synchronization with output from read/write head 2 of a pulse train
signal resulting from reading the successive [4E].sub.16
hexadecimal numbers from GAP 1. The resultant output signal from
sample-the signal read out during sampling, is supplied to the A/D
converter 43.
The index pulses P1 are also supplied via a signal input/output
terminal 63 of the input/output port 12 to the controller of the
host computer(not shown in the drawings), and the timing of these
index pulses P1 serves to determine the timings at which the
signals shown in FIG. 4 are recorded on the disk.
The A/D converter 43 supplies a sensing output signal S1 from
detection section 4 to the computation and control section 5.
Signal S1 is a digital signal, which represents the amplitude of
pulses in the signal which is read from the GAP 1 track
portion.
Fine adjustment of the radial position of the electromagnetic head
2 is performed by microstepping operation executed by access motor
1 under the control of rotation drive section 6. This microstepping
operation is illustrated in FIG. 5, in which an example of the read
signal level represented by signal S1 from A/D converter 43 is
plotted along the vertical axis, and corresponding microstep
displacement of the read/write head 2 is plotted along the
horizontal axis. Signal S1 varies successively in value as the
electromagnetic head 2 is displaced by microstep adjustment from a
standard position SP of an adjustment from a standard position SP
of a track, and attains a maximum value when the head 2 is
optimally positioned with respect to the target track, i.e. when
the off-track error is a minimum. The standard position SP is an
assumed position at which the head 2 should be correctly positioned
with respect to a track, in the absence of off-track errors. In the
preferred embodiment, the rotation drive section 6 consists of a
CPU (central processing unit) 61, and a drive circuit 62. During a
correction data acquisition operation, the CPU 61 causes the drive
circuit 62 to supply successively different predetermined levels of
drive current to the windings of access motor 1. Initiation of such
an operation is designated by a command signal S4 which is supplied
to the CPU 61 from a CPU 51 within the computation and control
section 5 (described hereinafter), and in response to these
successively varying levels of drive current applied to access
motor 1, the electromagnetic head 2 executes microstepping
operation radially across disk 3 through 15 microsteps. Preferably,
head 2 is successively stepped radially in one direction away from
position SP as a starting position, through 7 microsteps, then is
returned to position SP and is stepped radially in the opposite
direction through 7 microsteps. At each of these radial microstep
positions, sampling of the read-out signal S3 from head 2 is
performed at the timing of a P1 index pulse by sample-and-hold
circuit 42, to thereby obtain a digital output signal S1 from A/D
converter 43 which represents the amplitude of the sampled read
signal pulses. The microstep position at which the maximum
amplitude of signal S1 is obtained is the optimum radial position
of the head 2 with respect to the track in question, and the
difference (i.e. number of microsteps) between that position and
the standard position SP is the amount of off-track error. It can
thus be understood that this amount of off-track error, since it
represents a number of microsteps and a direction by which the head
2 must be moved radially from position SP to attain the correct
on-track position, constitutes a correction value for the track in
question. In the example shown in FIG. 5, this correction value
corresponds to movement of head 2 by 3 microsteps, in the radially
outward direction.
It has found that this sampling operation is preferably performed a
plurality of times for each of the microstep positions, and an
average value for signal S1 thereby obtained for each of these
positions, to achieve increased accuracy for signal S1.
The successive values of sensing output signal S1, obtained for
each of the microstep positions as described above, are supplied
from the detection section 4 through input port 52 of the
computation and control section 5 to the CPU 51. Based on a program
which is stored in the ROM 54, the CPU 51 determines the maximum
amplitude of the sensing signal S1, and thereby derives a
correction value for the track in question. This correction value
is then stored in a location corresponding to that track, in RAM
55.
Thus to execute a correction data acquisition operation, the
computation and control section 5 first issues a command signal S4
through output port 53 to a CPU 61 in the rotation drive section 6.
CPU 61 responds by causing a drive circuit 62 to drive the access
motor 1 to move the head 2 to the approximate position (i.e. the
standard position SP as described above) of the outer peripheral
track MOT. The correction value for track MOT is then derived as
described above, and stored in a predetermined address of RAM 55.
The head 2 is then moved to the reference position of track MIT,
and the above process repeated to derive and store a corresponding
correction value for that track.
The CPU 51 then computes optimum correction values for each of the
tracks on the disk which lie between track MIT, with these
correction values being computed based upon the correction values
(i.e. amounts of off-track error) obtained for tracks MIT and MOT
as described above. Computation of the optimum correction values
H.sub.N is performed using the following formula: ##EQU1##
Where N is the track number (designating the outermost track MOT as
having a track number of 0, the next radially inward track as
having a track number of 1, and so on successively), H.sub.N is the
correction value for the Nth numbered track, T.sub.A is the total
number of tracks, H.sub.MOT is the off-track error amount for the
outer peripheral track MOT, H.sub.MIT is the off-track error amount
for the inner peripheral track MIT. These correction values H.sub.N
are stored in predetermined respective addresses of RAM 55.
Subsequently, when access to a particular track is commanded by the
host computer, data (indicated in FIG. 3 as D.sub.t) which
specifies the required track is supplied from the host computer,
through port 12, to the CPU 51 of computation and control section 5
(via input port 52) and to the CPU 61 of rotation drive section 6.
The rotation drive section 6 responds by driving the access motor 1
to move head 2 to the standard position SP of the required track,
by normal stepping operation. Based on the input track data
D.sub.t, CPU 51 of computation and control section 5 then transfers
the correction value for that track into CPU 61 of the rotation
drive section, as signal S2, and CPU 61 controls drive circuit 62
to produce microstepping operation by access motor 1, by an amount
and in a direction which is determined by the correction value. The
off-track error in position of head 2 is thereby corrected, so that
head 2 is positioned accurately above the track which is to be
accessed.
The maximum range of movement of head 2 which can be produced by
such microstepping operation need only be extremely small. In the
example of FIG. 5, this range is only .+-.28 microns, i.e. each
microstep is equal to 4 microns of radial head movement.
In this way, the electromagnetic head 2 is positioned accurately
over a specific track and will thereby precisely follow that track
as the disk rotates.
If however the electromagnetic head 2 should thereafter enter an
off-track error condition during read-out of data from the
aforementioned track to the host computer, in spite of the
correction which has been applied as described above, then a signal
S12 indicating that a read error has occurred will be generated by
the host computer. Signal S12 is transferred through I/O port 12
and input port 52 to CPU 51 in computation and control section 5.
In response to signal S12, CPU 51 initiates operation in accordance
with a program which is stored in ROM 54, whereby the off-track
error amount for the track in question is measured and stored in
the address of RAM 55 corresponding to that track, as a new
correction value for the track (replacing the previously computed
correction value for the track in question). The derivation of such
an off-track error amount is performed in the same way as described
hereinabove with reference to tracks MOT and MIT. Upon completion
of acquisition of an updated correction value in this way, the
track is again accessed by the host computer, with the head now
accurately positioned with respect to the track.
In this way, the electromagnetic head 2 is held accurately on-track
for all of the tracks, by a form of continuously operating servo
control, which utilizes the read error detection capability that is
a standard function of computers which utilize such a disk drive
apparatus.
With the preferred embodiment, a cartridge insertion sensor 16, a
temperature sensor 17, a humidity sensor 18 and counter 57 are also
incorporated. When disk 3 (which forms part of a cartridge) is
inserted into the disk drive apparatus, the insertion is detected
by cartridge insertion sensor 16, which then produces a sensor
output signal S6. The temperature sensor 17 detects variations in
temperature within the disk drive apparatus, and produces a sensor
output signal S7 when a change in temperature occurs which exceeds
a predetermined amount. Similarly, the humidity sensor 18 detects
variations in humidity within the disk drive apparatus, and
produces a sensor output signal S8 when a change in humidity occurs
which is greater than a predetermined amount.
The counter 57 counts clock pulses P2 of fixed frequency, which are
supplied from pulse generator 56. When a predetermined number of
pulses have been counted, i.e. each time a predetermined time
interval has elapsed, counter 57 generates a counter output signal
S9.
The output signals S6, S7 and S8 from sensors 16, 17 and 18 are
supplied through the input port 52 of computation and control
section 5 to the OR gate 58. The counter output signal S9 is also
applied to an input of OR gate 58. Thus, each time that the
predetermined time interval has elapsed, or whenever disk 3 is
inserted into the apparatus, or when a change occurs in the
temperature or humidity within the disk drive apparatus which
exceeds a predetermined amount, then a gate output signal G1 is
produced from OR gate 58 and is transferred through AND gate 59 to
the CPU 51, if AND gate 59 is enabled at that time (as described
hereinafter). In response to this gate output signal G1, CPU 51
supplies the command signal S4 to CPU 61 of the rotation drive
section 6. A correction data acquisition operation is then
initiated, i.e. the off-track error quantities of the outer
peripheral track MOT and inner peripheral track MIT are again
detected, as described hereinabove. The computation and control
section then once more computes a new set of correction values
H.sub.N for all of the tracks of disk 3, based on the off-track
error quantities for the MOT and MIT, and stores these correction
values in the respective addresses of RAM 55, in place of the
previously derived correction values.
In this way, RAM 55 always has stored therein a set of correction
values H.sub.N which are optimized with regard to elapsed time and
to temperature and humidity changes.
In addition to the gate output signal G1, AND gate 59 also receives
as input a gate output signal G2 produced from AND gate 21, i.e.
transfer of an output signal from OR gate 58 through AND gate 59 is
controlled by signal G2. An AND gate 21 receives as inputs a
spindle motor drive signal S10 and the inverse of a selection
signal S11. These signals S10 and S11 are supplied through
terminals 20 and 19 respectively of input/output port 12 of the
disk drive apparatus. The spindle motor drive signal S10, supplied
from the host computer, is applied through drive circuit 22 as a
command signal to designate rotation of the spindle motor 7. The
selection signal S11 is a command signal which designates whether
or not the host computer has selected this disk drive
apparatus.
Thus, detection of the off-track error quantities and computation
of the respective correction values H.sub.N for the various tracks
is only performed while the following conditions are satisfied:
(a) the disk 3 is being rotated and,
(b) the disk drive apparatus (of FIG. 3) is not currently selected
by the host computer for write-in or read-out of data.
In the present embodiment, the rotation drive section 6 supplies
2-phase drive currents to the access motor 1. Normal stepping
operation is executed by successive alternations in polarity of the
drive current phases, as is well-known practice. During
microstepping operation, the polarities of the drive current phases
are held unchanged, but one current phase is varied in (absolute)
amplitude relative to the other. The preferred waveforms for these
drive current phases are as shown in FIG. 6, which shows the
variations in the absolute amplitude of the two drive current
phases (designated as i.sub.a and i.sub.b respectively) which are
required in order to execute the microstepping operations shown in
FIG. 5. As in FIG. 5, "SP" indicates the condition at which the
read/write head 2 is set at the standard position relative to a
track. In this condition, both of the drive current phases are at
the rated level thereof. To execute microstepping in the radially
outward direction, current phase i.sub.a is held constant, while
the amplitude of current phase i.sub.b is successively reduced in a
series of steps, which respectively decrease in magnitude in
accordance with a tangent curve as shown. Similarly, to execute
microstepping in the radially inward direction, current phase
i.sub.b is held constant, while current phase i.sub.a is
successively reduced in a series of steps, which respectively
decrease in magnitude in accordance with a tangent curve.
Such a drive method has the advantage that the total drive current
level which is supplied to the access motor 1 when the read/write
head is set to the standard position of a track (before
microstepping operation is initiated) can be fixed as the rated
current of the stepping motor. This current level ensures that the
maximum level of holding torque will be applied to the motor shaft,
upon completion of a step rotation, and thereby ensures rapid
attainment of a stable status of access motor 1 before a transition
to microstepping operation is initiated following completion of one
or more stepping operations.
With the prior art method of executing microstepping operation of
such a stepping motor, on the other hand, it is necessary that the
amplitude of one drive current phase, at an extremity of the range
of microstepping operation, be substantially higher than the
(common) amplitude of the two drive current phases at the center of
that range (i.e. the current level at which stepping operation
between successive tracks is performed). Specifically,
microstepping operation is executed by stepwise increments of on
drive current phase and simultaneous stepwise decrements of the
other phase, with the successive steps for one phase following a
sine curve and the successive steps for the other phase following a
cosine curve. As a result, it is necessary that the drive current
amplitude applied at the center of the microstepping range be
approximately 1/.sqroot.2 times the amplitude of the amplitude of
one of the current phases at an extremity of the microstepping
range. Thus, it is necessary to either:
(a) make the the drive current amplitude of both of the current
phases at the center of that range equal to 1.sqroot.2 times the
rated current (rather than equal to the rated current, as in the
example of FIG. 6), or:
(b) make the amplitude of one of the drive current phases
substantially higher than the rated current level, at an extremity
of the microstepping range (e.g. the 7th or -7th step in FIG.
6).
Either of these two alternatives has serious disadvantages, so that
the novel method proposed by the applicant and described above with
reference to FIG. 6 is highly advantageous, for attaining stable
high-speed stepping and microstepping movement of a read/write head
to thereby ensure an overall high speed of operation.
With the present invention, microstepping of the electromagnetic
head 2 by the drive current phases i.sub.A and i.sub.B is always
performed from the standard position SP as a starting point. Due to
this, the same drive method is employed during microstepping which
is performed during detection of the off-track error and
microstepping operation performed (to execute position error
correction) after access to a track has been initiated. This serves
to minimize the amount of hysteresis of the position at which the
electromagnetic head 2 is finally halted following access, and
thereby ensures maximum positioning accuracy.
It can be understood from the above that a disk drive apparatus
according to the present invention enables a read/write head to be
maintained correctly positioned with respect to a disk track,
without the necessity to provide dedicated servo tracks or embedded
servo data regions on the disk, since data indicating an amount of
off-track error is derived by read-out of a "gap", i.e. buffer
portion of standard format data, which is routinely recorded on
every track of a disk. Furthermore, continous monitoring of the
amount of off-track error while data is being read out from the
disk to a host computer is executed on the basis of read error
detection which is performed by the host computer itself. In this
way, a form of continuous servo control of the off-track error is
implemented.
It has been found that by employing a disk drive apparatus having
the configuration described above it is possible to increase the
maximum track density of a 3.5 inch disk from approximately 160 tpi
(tracks per inch) to approximately 270 tpi.
In the preferred embodiment, the detection output signal S1 is
derived by sampling the output signal from head 2 resulting from
reading the contents of the GAP 4 portion of the format data. This
is the longest of the gap regions in the format data, and hence
this method enables stable detection output to be obtained. However
it should be noted that the present invention is not limited to use
of that format data portion, and that it is possible to also
perform sampling of signals resulting from read-out of the GAP 2 or
GAP 3 portions of the format data, in which the same [4E].sub.16
data is repetitively recorded as in GAP 4. If this is done, then
correction values can be obtained for each track at several
positions along the track, whereby more accurate values of
correction data can be obtained for a disk which does not display
uniform degrees of expansion and contraction for different radial
directions along the disk surface. In this way, more accurate
on-track operation can be ensured.
Furthermore, with the described embodiment, correction values
H.sub.N for each of the tracks are obtained by detecting off-track
error quantities for the outer peripheral track MOT and inner
peripheral track MIT of disk 3, whereby accurately determined
correction values H.sub.N are obtained for all of the tracks.
However the invention is not limited to such an arrangement. For
example, it would be equally possible to also detect off-track
error quantities for a plurality of tracks which are positioned
between tracks MOT and MIT, and to utilize these off-track error
quantities in deriving correction values for the remaining tracks.
This would enable even more accurate correction values to be
obtained.
In the embodiment of FIG. 3, operation is described as being
controlled by separate CPUs 51 and 61. However it will be apparent
that in a practical system, the functions of both of these CPUs can
be combined in a single system. The CPUs 51 and 61 and the
associated ROM 54, drive circuit 62, etc. can thus be collectively
defined as computation and control means for controlling the
overall operation of the disk drive apparatus and the computation
of correction values, and are so defined in the appended
claims.
Furthermore, although in the described embodiment the index pulses
P1 are derived by an opto-electric system linked to the shaft of
the spindle motor which drives the disk, the invention is not
limited to such an arrangement. It would be equally possible to
employ other means for generating index pulses, such as optical
sensing of the position of an index aperture formed in each disk,
for example.
Thus, although the present invention has been described in the
above with reference to specific embodiments, it should be noted
that various changes and modifications to the embodiments may be
envisaged, which fall within the scope claimed for the invention as
set out in the appended claims. The above specification should
therefore be interpreted in a descriptive and not in a limiting
sense.
* * * * *